Main Sequence Turnoff

The Main Sequence Turnoff is a point in a star cluster's color-magnitude diagram that indicates the age of the cluster. It marks the stage where the most massive stars have exhausted their core hydrogen fuel and begin evolving into later stages like giant stars. Since massive stars burn through their fuel faster, their departure from the main sequence happens earlier. By identifying this turnoff point, astronomers determine the cluster's age, as it reflects the lifetime of the stars just leaving the main sequence. This process helps in understanding the age and evolution of star clusters.